Vibration-insulating rubber composition

ABSTRACT

A vibration-insulating rubber composition includes: a rubber component (A) that is composed of an isoprene-based rubber; a rubber component (B) that is composed of a butadiene-based rubber; carbon black that is present mainly in the rubber component (B); and silica that is present mainly in the rubber component (A). The rubber composition exhibits improved durability without suffering from deterioration of vibration-insulation characteristics.

TECHNICAL FIELD

The present invention relates to a vibration-insulating rubber composition.

BACKGROUND ART

Conventionally, a vibration-insulating rubber used in an engine mount or the like of an automobile is required to have vibration-insulating performance for reducing vibration and noise of an engine, heat resistance, fatigue resistance and the like. In addition, in point of the vibration-insulating performance, the smaller a spring constant in a vibrational state (dynamic spring constant), the better; on the other hand, the larger a static spring constant that indicates supporting stiffness, the better; moreover, it can be said that the vibration-insulating rubber having a smaller dynamic multiplication (dynamic spring constant/static spring constant), which is a ratio between the dynamic spring constant and the static spring constant, provides more excellent vibration-insulating performance.

As a specific example of such a vibration-insulating rubber, for example, in Patent Document 1, there is described a rubber composition for engine mounts that contains a rubber component consisting mainly of at least one diene rubber and silica fine particles having a BET specific surface area of 40-170 m²/g.

In Patent Document 2, a vulcanized body of vibration-insulating rubber composition is disclosed, in which natural silica treated by a silane coupling agent is combined with rubber compositions such as natural rubber, butadiene rubber and styrene butadiene rubber, and a mixture of quartz powder having globular structure of fine particles and kaolinite having hexagonal plate-shaped grain structure is used for natural silica.

In Patent Document 3, there is described a vibration-insulating rubber composition containing a rubber component (A), hydrophobically treated silica (B) and a silane-coupling agent (C), in which, as the hydrophobically treated silica (B), it is preferable to blend silicone oil of 0.1 pts.wt. to 50 pts.wt. having dynamic viscosity in a range of 10⁻⁶ m²/s to 1 m²/s with wet method silica of 100 pts.wt. having nitrogen-absorbing specific surface area (BET method) in a range of 30 m²/g to 230 m²/g for surface treatment.

CITATION LIST Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open Publication No. 11-193338

Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2002-098192

Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2006-037002

SUMMARY OF INVENTION Technical Problem

Incidentally, to achieve vibration-insulating characteristics (low dynamic multiplication) of a vibration-insulating rubber, there is a tendency to use a filler of a large diameter. However, the large-diameter filler has low reinforcing property, and has a problem of deterioration of durability in a long-term use. On the other hand, if a filler of a small diameter having high reinforcing property is used to increase the durability, there is a tendency to reduce the vibration-insulating characteristics. As things stand, in this way, the vibration-insulating characteristics and the durability of the vibration-insulating rubber are in a trade-off relationship, and it is difficult to achieve both.

Moreover, for increasing product life of the vibration-insulating rubber, it is necessary to improve the durability or heat resistance. Especially, the heat resistance is important. Usually, for improving the durability of the vibration-insulating rubber, it is desirable to have a lower stress when the same displacement is applied. However, on the occasion of vulcanizing, if an amount of use of a vulcanizing agent is reduced to decrease the vulcanizing density, there is a tendency to deteriorate the dynamic multiplication. On the other hand, if a combined amount of a reinforcing agent is reduced, the static spring constant becomes small; and accordingly, for example, displacement in supporting an automobile engine or the like is increased to thereby deteriorate the durability. In particular, in a case where the heat resistance is insufficient, there is a problem of impossibility of maintaining the vibration-insulating characteristics together with the durability.

An object of the present invention is to improve durability of a vibration-insulating rubber while maintaining vibration-insulating characteristics.

An object of the present invention is to improve heat resistance of a vibration-insulating rubber while maintaining vibration-insulating characteristics.

Solution to Problem

By the present invention, a vibration-insulating rubber composition according to any of the following first to twelfth aspects is provided.

According to a first aspect of the present invention, there is provided a vibration-insulating rubber composition including: a rubber component (A) composed of an isoprene-based rubber; a rubber component (B) composed of a butadiene-based rubber; a carbon black that is present mainly in the rubber component (B); and a silica that is present mainly in the rubber component (A).

According to a second aspect of the present invention, in the vibration-insulating rubber composition of the first aspect, at least 70 wt % of a total amount of the carbon black is present in the rubber component (B), and at least 70 wt % of a total amount of the silica is present in the rubber component (A).

According to a third aspect of the present invention, in the vibration-insulating rubber composition of any one of the first and second aspects, the silica is modified by a silane coupling agent.

According to a fourth aspect of the present invention, in the vibration-insulating rubber composition of the third aspect, the silane coupling agent is a polysulfide-based silane coupling agent.

According to a fifth aspect of the present invention, in the vibration-insulating rubber composition of any one of the first to fourth aspects, an amount ratio between the rubber component (A) and the rubber component (B) (rubber component (A)/rubber component (B)) is 90/10 to 30/70 (however, a total of the rubber component (A) plus the rubber component (B) equals 100 wt %).

According to a sixth aspect of the present invention, there is provided a vibration-insulating rubber composition including: a total amount of an isoprene-based rubber and a butadiene-based rubber that equals 100 pts.wt.; a carbon black of 5 pts.wt. to 60 pts.wt.; and a silica of 5 pts.wt. to 60 pts.wt., wherein at least 70% of a total amount of the carbon black is unevenly distributed in the butadiene-based rubber, and at least 70% of a total amount of the silica is unevenly distributed in the isoprene-based rubber.

According to a seventh aspect of the present invention, there is provided a vibration-insulating rubber composition including: a rubber component including an isoprene-based rubber and a butadiene-based rubber; and a reinforcing agent component including a carbon black and a silica, the rubber component and the reinforcing agent component being compounded, wherein the silica in the reinforcing agent component includes: a silica (A) in which a surface of a silica particle is surface-treated by a polysulfide-based silane coupling agent; and a silica (B) in which a surface of a silica particle is surface-treated by a silane-based surface treatment agent.

According to an eighth aspect of the present invention, in the vibration-insulating rubber composition of the seventh aspect, the silane-based surface treatment agent in the silica (B) is silane containing a hydrocarbon radical.

According to a ninth aspect of the present invention, in the vibration-insulating rubber composition of any one of the seventh and eighth aspects, an amount ratio between the silica (A) and the silica (B) in the silica (silica (A)/silica (B)) is (90/10) to (40/60) (however, a total of the silica (A) plus the silica (B) equals 100 wt %).

According to a tenth aspect of the present invention, in the vibration-insulating rubber composition of any one of the seventh to ninth aspects, the silica (B) in the silica is a hydrophobically modified silica obtained by processing a surface of silica by alkylsilane.

According to an eleventh aspect of the present invention, in the vibration-insulating rubber composition of any one of the seventh to tenth aspects, an amount ratio between the isoprene-based rubber and the butadiene-based rubber in the rubber component (isoprene-based rubber/butadiene-based rubber) is (90/10) to (30/70) (however, a total of the isoprene-based rubber plus the butadiene-based rubber equals 100 wt %).

According to a twelfth aspect of the present invention, there is provided a vibration-insulating rubber composition including: a total amount of an isoprene-based rubber and a butadiene-based rubber that equals 100 pts.wt.; a carbon black of 5 pts.wt. to 60 pts.wt.; and a silica of 5 pts.wt. to 60 pts.wt., wherein, against a total amount of the silica, a silica (A) that is surface-treated by a polysulfide-based silane coupling agent represents 40 wt % to 90 wt %, and a silica (B) that is surface-treated by silane containing a hydrocarbon radical represents 10 wt % to 60 wt % (however, a total of the silica (A) plus the silica (B) equals 100 wt %).

Advantageous Effects of Invention

According to the present invention, it is possible to improve durability of a vibration-insulating rubber while maintaining vibration-insulating characteristics.

Moreover, according to the present invention, it is possible to improve heat resistance of a vibration-insulating rubber while maintaining vibration-insulating characteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for illustrating a specimen used in a durability test; and

FIG. 2 is a photograph of a transmission electron microscope (TEM) of a rubber composition in Example 2.

DESCRIPTION OF EMBODIMENTS

Hereinafter, modes for embodying the present invention will be described (hereinafter, exemplary embodiments). It should be noted that the present invention is not limited to the following exemplary embodiments, but may be practiced as various modifications within the scope of the gist of the invention.

<Vibration-Insulating Rubber Composition (1)>

In the present invention, a vibration-insulating rubber composition to which a first exemplary embodiment is applied (hereinafter, referred to as “vibration-insulating rubber composition (1)”) includes a rubber component (A) composed of an isoprene-based rubber, a rubber component (B) composed of a butadiene-based rubber, carbon black that is present mainly in the rubber component (B) and a silica that is present mainly in the rubber component (A). Hereinbelow, each component will be described.

<Isoprene-Based Rubber (Rubber Component (A))>

As an isoprene-based rubber used in the exemplary embodiment, a natural rubber and a polyisoprene rubber (hereinafter, referred to as IR in some cases) are provided. As the polyisoprene rubber, a high cis-polyisoprene rubber having cis-1,4 coupling of about 96% or more and a low cis-polyisoprene rubber having cis-1,4 coupling of the order of 94% are provided. A Mooney viscosity (ML_(1+4, 100° C.)) of the polyisoprene rubber is normally 50 to 200, and preferably 60 to 150. In addition, these diene-based rubbers can be used irrespective of the Mooney viscosity before oil extension as long as the Mooney viscosity after oil extension is within the above-described range.

A Mooney viscosity (ML_(1+4, 100° C.)) of a natural rubber is normally 10 to 200, and preferably 30 to 100.

<Butadiene-Based Rubber (Rubber Component (B))>

As a butadiene-based rubber (hereinafter, referred to as BR in some cases) used in the exemplary embodiment, for example, a high cis-polybutadiene rubber having cis-1,4 coupling of about 90% or more and a high vinyl-polybutadiene rubber having 1,2-coupling of about 10% or more are provided. Among them, the high vinyl-polybutadiene rubber is preferable because carbon black is selectively dispersed with ease. A Mooney viscosity (ML_(1+4, 100° C.)) of the polybutadiene rubber is normally 10 to 100, and preferably 30 to 70.

An amount ratio between the rubber component (A) and the rubber component (B) (rubber component (A)/rubber component (B)) included in the vibration-insulating rubber composition (1) to which the exemplary embodiment is applied is 90/10 to 30/70, preferably 80/20 to 40/60, and more preferably 80/20 to 50/50 (however, a total of the rubber component (A)+the rubber component (B) is equal to 100 wt %). If the amount of the rubber component (A) included in the vibration-insulating rubber composition (1) is excessively large, there is a tendency to increase the dynamic multiplication. On the other hand, if the amount of the rubber component (A) is excessively small, there is a tendency to deteriorate the durability.

<Carbon Black>

The carbon black used in the exemplary embodiment is not particularly limited as long as it is known as a normal reinforcing agent for rubbers. For example, furnace black, channel black, thermal black and so forth are provided.

<Silica>

The silica used in the exemplary embodiment is not particularly limited as long as it is known as a normal reinforcing agent for rubbers (white carbon). For example, silicic acid anhydride obtained by a dry method, silicic acid hydrate obtained by a wet method, and further, synthetic silicate are provided.

A BET specific surface area of a silica particle used in the exemplary embodiment is 20 m²/g to 200 m²/g and preferably 50 m²/g to 150 m²/g. It should be noted that the BET specific surface area is measured based on JIS-K-6217-1997 “Testing methods of fundamental characteristics of carbon black for rubber industry”. If the BET specific surface area of the silica particle is excessively small, there is a tendency to deteriorate the reinforcing property. On the other hand, if the BET specific surface area of the silica particle is excessively large, there is a tendency to increase the dynamic multiplication.

(Surface-Treated Silica)

The surface of the particle of silica used in the exemplary embodiment is preferably subjected to surface treatment with a silane coupling agent. The surface treatment method of the surface of the silica particle is not particularly limited; for example, a method in which the silica particles and the silane coupling agents are brought into contact in advance, a method in which the silica particles and the silane coupling agents are kneaded together with the rubber components (A), (B) and other compounding agents, and the like are provided.

As the silane coupling agents used for the surface treatment of silica, compounds including portions of functional groups for surface modification of silica particles, alkoxide groups that react with hydroxyl groups of the surface of the silica particles, amino groups and the like are provided. As a silane coupling agent including alkyl groups, specific examples include: methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, phenyltrimethoxysilane, octyltrimethoxysilane, octadecyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, octyltriethoxysilane and octadecyltriethoxysilane.

Specific examples having other functional groups include: 3-mercaptopropyltrimethoxysilane, (mercaptomethyl)methyldiethoxysilane, (mercaptomethyl)dimethylethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, bis[3-(triethoxysilyl)propyl]tetrasulfide, 3-isocyanatopropyltriethoxysilane, N-[(3-trimethoxysilyl)propyl]ethylenediamine sodium triacetate, N-(triethoxysilylpropyl)urea, 3-chloropropyltriethoxysilane, diethylphosphate ethyltriethoxysilane, trimethoxysilylpropylisothiouronium chloride, methyl[2-(3-trimethoxysilylpropylamino)ethylamine]-3-propionate and 3-aminopropyltriethoxysilane.

Of the above-described silane coupling agents, in the case of adding a hydrophobic nature to the particles, the silane coupling agents having a molecular structure including sulfur atoms or nitrogen atoms are preferred because of their high treatment effect and the like. As such silane coupling agents, for example, silane coupling agents including nitrogen atoms such as N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane and γ-aminopropyltriethoxysilane, and polysulfide-based silane coupling agents such as bis(3-triethoxysilypropyl)disulfide, bis[3-(triethoxysilyl)propyl]tetrasulfide and γ-trimethoxysilylpropylbenzothiazyl tetrasulfide are provided. Of these, the polysulfide-based silane coupling agents such as γ-mercaptopropyltrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide can be preferably used.

Moreover, in general, as long as affinity for silica particles is shown after hydrolyzing, other metal alkoxide-based coupling agents or mixture of these with silane coupling agents can be used. For example, titanate coupling agents such as isopropyltriisostearoyl titanate and isopropyltrioctanoyl titanate, zirconate coupling agents such as zirconium lactate and acetylacetone zirconium butyrate, and zircoalminate-based coupling agents and so on can be provided.

(Uneven Distribution Rate of Carbon Black and Silica)

In the vibration-insulating rubber composition (1) to which the exemplary embodiment is applied, at least 70 wt % of a total amount of carbon black is present in the rubber component (B) (butadiene-based rubber). Further, on the other hand, at least 70 wt % of a total amount of silica included in the compound is present in the rubber component (A) (isoprene-based rubber). In the exemplary embodiment, since carbon black and silica are thus unevenly distributed in the butadiene-based rubber and the isoprene-based rubber selectively, respectively, both rubber components (A) and (B) have reinforced structures, and thereby durability thereof is improved.

Though the reason why carbon black and silica are unevenly distributed in the rubber component (B) and the rubber component (A) selectively, respectively, in the vibration-insulating rubber composition (1) to which the exemplary embodiment is applied, is not clear; however, it can be assumed as follows. That is, it is considered that affinity for or interaction with the rubber component (B) (butadiene-based rubber) of the carbon black is large compared to affinity for or interaction with the rubber component (A) (isoprene-based rubber). On the other hand, for example, it is considered that affinity for or interaction with the rubber component (A) (isoprene-based rubber) of the silane coupling agent including sulfur atoms such as polysulfide-based silane coupling agent is large compared to affinity for or interaction with the rubber component (B) (butadiene-based rubber). Accordingly, it is considered that, within a range of the ratio between the rubber components and the combined amount of the reinforcing agent in the vibration-insulating rubber composition (1) to which the exemplary embodiment is applied, carbon black and silica are unevenly distributed in the rubber component (B) and the rubber component (A) selectively, respectively.

Here, the rate at which the carbon black and the silica are unevenly distributed in the butadiene-based rubber and the isoprene-based rubber selectively, respectively (hereinafter, referred to as “uneven distribution rate” in some cases), is obtained by the following operations.

A rubber composition including the rubber component (A), the rubber component (B), the carbon black and the silica is prepared, and is cut with a microtome to prepare slices with a thickness of 0.1 μm. The slice is observed as a specimen by a transmission electron microscope (TEM) while regarding particles having a particle diameter of about 0.8 μm to about 1.2 μm as carbon black and particles having a particle diameter of about 10 nm to about 40 nm as silica. On that occasion, in an electronic image of the rubber composition, the number of particles of carbon black and silica present in each of the phase of the rubber component (A) (isoprene-based rubber) and the phase of the rubber component (B) (butadiene-based rubber) is measured. Then, in each of the phase of the rubber component (A) (isoprene-based rubber) and the phase of the rubber component (B) (butadiene-based rubber), the ratio between the number of particles of carbon black and the number of particles of silica is obtained, and thereby the uneven distribution rate of carbon black and silica in each phase was obtained. It should be noted that, in the exemplary embodiment, the number of samples is 30 (n=30).

If an amount of silica unevenly distributed in the rubber component (A) (isoprene-based rubber) is excessively small against the total amount of silica included in the composition, there is a tendency to deteriorate the durability because the rubber component (A) is not sufficiently reinforced. On the other hand, if an amount of silica unevenly distributed in the rubber component (A) (isoprene-based rubber) is excessively large, there is a tendency to deteriorate dynamic characteristics and the durability because dispersing property becomes poor.

If an amount of carbon black unevenly distributed in the rubber component (B) (butadiene-based rubber) is excessively small against the total amount of carbon black included in the composition, there is a tendency to deteriorate the durability because the rubber component (B) is not sufficiently reinforced. On the other hand, if an amount of carbon black unevenly distributed in the rubber component (B) (butadiene-based rubber) is excessively large, there is a tendency to deteriorate dynamic characteristics and the durability because dispersing property becomes poor.

<Vibration-insulating Rubber Composition (2)>

In the present invention, in a vibration-insulating rubber composition to which a second exemplary embodiment is applied (hereinafter, referred to as “vibration-insulating rubber composition (2)”), a rubber component including an isoprene-based rubber and a butadiene-based rubber and a reinforcing agent component including carbon black and silica are compounded, in which silica in the reinforcing agent component includes silica (A) that is surface-treated by a polysulfide-based silane coupling agent and silica (B) that is surface-treated by a silane-based surface treatment agent. Hereinbelow, each component will be described.

An amount ratio between the isoprene-based rubber and the butadiene-based rubber (isoprene-based rubber/butadiene-based rubber) included in the vibration-insulating rubber composition (2) to which the exemplary embodiment is applied is (90/10) to (30/70), preferably (80/20) to (40/60), and more preferably (80/20) to (50/50) (however, a total of the isoprene-based rubber+the butadiene-based rubber is equal to 100 wt %). If the amount of the rubber component (A) included in the vibration-insulating rubber composition (2) is excessively large, there is a tendency to increase the dynamic multiplication. On the other hand, if the amount of the rubber component (A) is excessively small, there is a tendency to deteriorate the durability.

<Reinforcing Agent Component> (Carbon Black)

An amount of usage of carbon black included in the vibration-insulating rubber composition (2) is not particularly limited. In the exemplary embodiment, against a total amount of the isoprene-based rubber and the butadiene-based rubber included in the rubber component that equals 100 pts.wt., carbon black is used in a range of 5 pts.wt. to 60 pts.wt., preferably in a range of 7 pts.wt. to 50 pts.wt., and more preferably in a range of 7 pts.wt. to 40 pts.wt.

(Silica)

Silica included in the reinforcing agent component used in the vibration-insulating rubber composition (2) includes silica (A) which is silica particles known as a usual reinforcing agent for rubbers (white carbon) surface-treated by the polysulfide-based silane coupling agent and silica (B) which is silica particles known as a usual reinforcing agent for rubbers (white carbon) surface-treated by the silane-based surface treatment agent.

(Silica A)

Silica A included in silica used in the exemplary embodiment is silica particles surface-treated by the polysulfide-based silane coupling agent. The surface treatment method of the surface of the silica particle is not particularly limited; for example, a method in which the silica particles and the silane coupling agents are brought into contact in advance, a method in which the silica particles and the silane coupling agents are kneaded together with the rubber component, carbon black and other compounding agents are provided.

As the polysulfide-based silane coupling agents used for surface treatment of silica, for example, 3-mercaptopropyltrimethoxysilane, (mercaptomethyl)methyldiethoxysilane, (mercaptomethyl)dimethylethoxysilane, bis[3-(triethoxysilyl)propyl]tetrasulfide, bis[3-(triethoxysilyl)propyl]disulfide and γ-trimethoxysilylpropylbenzothiazyl tetrasulfide are provided. Of these, bis[3-(triethoxysilyl)propyl]tetrasulfide and bis[3-(triethoxysilyl)propyl]disulfide are preferred. The surface of the particle of silica that is surface-treated by the silane coupling agent having molecular structure including sulfur atoms is provided with a hydrophobic nature.

The silica particles (silica A) surface-treated by use of such polysulfide-based silane coupling agents are commercially available. For example, CABRUS 2A, CABRUS 2B and CABRUS 4 manufactured by DAISO Co., Ltd., Si-75 and Si-69 manufactured by Degussa, A-1289 manufactured by GE silicone, KBE-846 manufactured by Shin-Etsu Chemical Co., Ltd. and the like are provided. These can be used individually or in combination.

(Silica B)

Silica B included in silica used in the exemplary embodiment is silica particles surface-treated by the silane-based surface treatment agent. Silica B is not particularly limited as silica subjected to surface treatment. In the exemplary embodiment, silicic acid anhydride obtained by a dry method (dry process silica) is preferred. Here, dry process silica is silicon dioxide generated by forming surface-modified silicon compound such as silicon dimethyl chloride and silicon tetrachloride under the condition of vapor phase hydrolysis at high temperature. By surface treatment of the surface of the particle of dry process silica by use of the silane-based surface treatment agent, hydrophobically modified silica, in which a hydrophobic nature is provided to the surface of the silica particle, is obtained.

As the silane-based surface treatment agent, organic silane, alkylsilane (silane containing a hydrocarbon radical), disilazan, alkylchlorosilane and the like are provided. Of these, alkylsilane (silane containing a hydrocarbon radical) is preferred.

Specifically, as organic silane and alkylsilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, n-octyltriethoxysilane, phenyltriethoxysilane, polytriethoxysilane; trialkoxyarylsilane; isooctyltrimethoxy-silane, N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate, polydialkylsiloxane containing polydimethylsiloxane, arylsilane containing substituted arylsilane and non-substituted arylsilane, alkylsilane containing methoxy substituted alkylsilane and hydroxyl substituted alkylsilane and the like are provided.

As alkylchlorosilane, for example, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, octylmethyldichlorosilane, octyltrichlorosilane, octadecylmethyldichlorosilane, octadecyltrichlorosilane and the like are provided. Moreover, as other compounds, vinylsilane such as vinyltrichlorosilane, vinylmethyldichlorosilane, vinyldimethylchlorosilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane and vinyldimethylethoxysilane can be provided.

As specific trade names, the products by Degussa, such as Aerosil DT4, Aerosil NA200Y, Aerosil NA5OH, Aerosil NA50Y, Aerosil NAX50, Aerosil R104, Aerosil R106, Aerosil R202, Aerosil R202W90, Aerosil R504, Aerosil R711, Aerosil R700, Aerosil R7200, Aerosil R805, Aerosil R805VV90, Aerosil R812, Aerosil R812S, Aerosil R816, Aerosil R8200, Aerosil R972, Aerosil R972V, Aerosil R974, Aerosil RA200HS, Aerosil RX200, Aerosil RX300, Aerosil RX50, Aerosil RY200, Aerosil RY200S, Aerosil RY300 and Aerosil RY50, and the like are shown as examples.

In the exemplary embodiment, an amount ratio between silica (A) and silica (B) (silica (A)/silica (B)) included in silica as the reinforcing agent component is in a range of (90/10) to (40/60), and preferably in a range of (80/20) to (50/50) (however, a total of silica (A)+silica (B) is equal to 100 wt %).

If an amount of silica (A) in silica as the reinforcing agent component is excessively large (an amount of silica (B) is excessively small), there is a tendency to deteriorate heat resistance by the polysulfide-based silane coupling agent. On the other hand, if an amount of silica (A) is excessively small (an amount of silica (B) is excessively large), there is a tendency to reduce silica that is chemically combined with rubber, and thereby to deteriorate dynamic characteristics.

An amount of usage of silica included in the vibration-insulating rubber composition (2) is not particularly limited. In the exemplary embodiment, against a total amount of the isoprene-based rubber and the butadiene-based rubber included in the rubber component that equals to 100 pts.wt., silica is used in a range of 5 pts.wt. to 60 pts.wt., preferably in a range of 7 pts.wt. to 50 pts.wt., and more preferably in a range of 7 pts.wt. to 40 pts.wt.

(Other Rubber Components)

As necessary, it is possible to mix other rubbers into the vibration-insulating rubber composition (1) or (2) to which the exemplary embodiment is applied. As such rubbers, for example, emulsion polymerized styrene butadiene rubber (SBR), solution polymerized SBR, acrylonitrile-butadiene copolymer rubber (NBR), hydrogenated acrylonitrile-butadiene copolymer rubber (HNBR), ethylene-α-olefin-based copolymer rubber (EPR, EPDM) and the like are provided.

(Other Reinforcing Agents)

As necessary, it is possible to mix other reinforcing agents into the vibration-insulating rubber composition (1) or (2) to which the exemplary embodiment is applied. As such reinforcing agents, for example, insulating metallic oxides such as tin oxide, zinc oxide, aluminum oxide, molybdenum oxide, magnesium oxide, calcium oxide and lead oxide; metallic hydroxides such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, zinc hydroxide and lead hydroxide; carbonates such as magnesium carbonate, aluminum carbonate, calcium carbonate and barium carbonate; silicates such as magnesium silicate, calcium silicate, sodium silicate and aluminum silicate; sulfates such as aluminum sulfate, calcium sulfate and barium sulfate; metallic powder such as iron powder; conductive fiber such as carbon fiber; diatomaceous earth; asbestos; lithopone (zinc sulfide/barium sulfate); graphite; fluorocarbon; calcium fluoride; wollastonite; glass powder and the like are provided.

(Other Compounding Agents)

As necessary, it is possible to mix other compounding agents that are known as ordinary compounding agents for rubbers into the vibration-insulating rubber composition (1) or (2) to which the exemplary embodiment is applied. As such compounding agents, for example, various kinds of chemical agents such as a vulcanizing agent, a vulcanization accelerator, oil, an antioxidant, a stabilizing agent and a coloring agent can be used as necessary.

As the vulcanizing agents, sulfur-based vulcanizing agents, organic peroxides, bismaleimide compounds and the like are provided. As the sulfur-based vulcanizing agents, sulfurs such as powdered sulfur and precipitated sulfur, 4,4′-dithiomorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, organic sulfur compound such as polymeric polysulfide, and the like are provided.

In the case of using the sulfur-based vulcanizing agents, usually, the vulcanization accelerator and a vulcanization accelerating auxiliary are used in combination. As the vulcanization accelerator, a sulfur-containing accelerator of thiuram series, sulfonamide series, thiazole series, dithiocarbamate series, thiourea series and the like; a nitride-containing accelerator of aldehyde-ammonia series, aldehyde-amine series, guanidine series and the like; and so forth are provided.

Of the vulcanization accelerators, the thiuram-based accelerator is preferable. Specific examples of the thiuram-based accelerators include, for example, tetramethylthiuram disulfide (TT) (TMTD), tetramethylthiuram monosulfide (TS) (TMTM), tetraethylthiuram disulfide (TET) (TETD), tetrabutylthiuram disulfide (TBT) (TBTD), dipentamethylenethiuram hexasulfide (TRA) (DPW) and tetrabenzylthiuram disulfide. Moreover, as the vulcanization accelerating auxiliary, zinc flower, magnesium oxide and the like are provided. An amount of usage of the vulcanization accelerator and vulcanization accelerating auxiliary is not particularly limited, and is determined in accordance with the kind of the sulfur-based vulcanizing agent.

As the organic peroxide, dialkylperoxide, diacylperoxide, peroxyester and the like are provided. As the dialkylperoxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,3-bis(t-butylperoxyisopropyl)benzene and the like are provided. As the diacylperoxide, benzoyl peroxide, isobutyryl peroxide and the like are provided. As the peroxyester, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxyisopropyl carbonate and the like are provided.

In the case of using the organic peroxide, usually, crosslinking auxiliary agent is used in combination. As the crosslinking auxiliary agent, triallyl cyanurate, trimethylolpropane trimethacrylate, N,N′-m-phenylenebismaleimide and the like are provided. An amount of usage of the crosslinking auxiliary agent is not particularly limited, and is determined in accordance with the kind of a crosslinking agent.

As the bismaleimide compound, N,N′-(m-phenylene)bismaleimide, N,N′-(p-phenylene)bismaleimide, N,N′-(o-phenylene)bismaleimide, N,N′-(1,3-naphthylene)bismaleimide, N,N′-(1,4-naphthylene)bismaleimide, N,N′-(1,5-naphthylene)bismaleimide, N,N′-(3,3′-dimethyl-4,4 ‘-biphenylene)bismaleimide, N,N′-(3,3′-dichloro-4,4′-biphenylene)bismaleimide and the like are provided.

In the case of using the bismaleimide compound, for example, oximes such as p-quinonedioxime, p,p′-dibenzoyl quinonedioxime, and tetrachloro-p-benzoquinone; morpholine compounds such as 4,4′-dithiodimorpholine, N-ethylmorpholine, and morpholine; and the like are used in combination as necessary.

An compounding amount of the vulcanizing agent is not particularly limited; however, usually, against a total amount of the rubber component (A) and the rubber component (B) that equals to 100 pts.wt., the compounding amount of the vulcanizing agent is in a range of 0.1 pts.wt. to 10 pts.wt., preferably in a range of 0.3 pts.wt. to 7 pts.wt., and more preferably in a range of 0.5 pts.wt. to 5 pts.wt.

As the oil, for example, extender oil which is processing oil such as aromatic oil, naphthenic oil and paraffinic oil; a plasticizing agent such as dioctyl phthalate; a wax such as a paraffin wax and a carnauba wax; and the like are provided.

Moreover, to improve the heat resistance of the vibration-insulating rubber that is used under high temperature atmosphere for a long time, it is preferable to compound an antioxidant into the vibration-insulating rubber composition (1) or (2) to which the exemplary embodiment is applied. As the antioxidant, for example, an amine-ketone series such as poly-(2,2,4-trimethyl-1,2-dihydroquinone); an amine series such as N-phenyl-N′-isopropyl-p-phenylenediamine, and N-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine; a phenol series such as 2,2′-methylene-bis(4-ethyl-6-t-buthylphenol); 2-mercaptobenzimidazole; and the like are provided.

A compounding amount of the antioxidant is not particularly limited; however, usually, against a total amount of the rubber component (A) and the rubber component (B) that equals to 100 pts.wt., the compounding amount of the antioxidant is in a range of 0.1 pts.wt. to 10 pts.wt., preferably in a range of 0.3 pts.wt. to 7 pts.wt., and more preferably in a range of 0.5 pts.wt. to 5 pts.wt.

(Producing Method of Vibration-Insulating Rubber Composition)

A producing method of the vibration-insulating rubber composition (1) or (2) to which the exemplary embodiment is applied is not particularly limited; however, usually, produced by kneading and mixing the isoprene-based rubber and the butadiene-based rubber, other rubber such as the natural rubber as necessary, carbon black and silica, the silane coupling agent, other reinforcing agent and other compounding agent such as vulcanizing agent as necessary by a mixer such as a roller or a Banbury mixer.

The vibration-insulating rubber composition (1) or (2) that is combined with the above-described vulcanizing agent and is vulcanizable is molded into a predetermined shape by a conventionally known molding method such as injection molding and extrusion molding, and is vulcanized by a method such as steam vulcanization. The vulcanizing temperature of the vibration-insulating rubber composition is not particularly limited; however, usually, 100° C. to 200° C., preferably 130° C. to 190° C., and more preferably 140° C. to 180° C. In addition, the vulcanizing time is changed in accordance with the vulcanizing method, temperature, shape and the like, and is not particularly limited. The time is usually one minute or more and five hours or less. It should be noted that, as necessary, secondary vulcanization may be performed. The vulcanizing method can be selected from the methods usually used for vulcanization of rubber, such as press heating, steam heating, oven heating and hot air heating.

EXAMPLES

Hereinafter, the present invention will be described in more detail based on examples. It should be noted that the present invention is not limited to the examples. Note that all parts and % in the examples and comparative examples are on a weight basis, except where specifically noted.

(Durability Test)

FIG. 1 is a diagram illustrating a specimen used in a durability test. The specimen 10 shown in FIG. 1 is configured with: a metal internal cylinder 11 that has a cylindrical shape and is laterally mounted; a metal external cylinder 12 that has a cylindrical shape and encloses the metal internal cylinder 11 axially in parallel therewith; and a rubber elastic body 13 that is formed between the metal internal cylinder 11 and the metal external cylinder 12 and integrally combines both cylinders by means of vulcanization adhesion. The metal internal cylinder 11 has an outer diameter of 30 mm and a length of 65 mm, and an inner diameter of a bearing portion 14, into which a shaft member of a later-described vibration tester is inserted, is 15 mm. The metal external cylinder 12 has an outer diameter of 75 mm and a length of 45 mm.

The rubber elastic body 13 was prepared by vulcanization molding of a rubber composition having a compounding composition shown in Table 1, which will be later described, under the condition of 170° C. by two hours.

By use of the specimen 10, a durability test was performed with a vibration tester (manufactured by KYB Co., Ltd.: a fatigue tester) (not shown). The specimen 10 is fixed to the vibration tester by inserting the shaft member of the vibration tester into the bearing portion 14 of the specimen 10. Next, at room temperature, vibration was applied in an axially perpendicular direction of the metal internal cylinder 11 (direction of arrow A) with a frequency of 5 Hz and a load of +1670N to −1000N, to measure the number of excitation until the time when cracking was observed on a surface of the rubber elastic body 13 (units: 10000 times). The larger the numerical value, the more excellent in durability.

(Dynamic Characteristics Test)

Each of rubber compositions with compounds shown in Table 1 and Table 2, which will be later described, was heated at 170° C. for 25 minutes, and in conformity with JIS K 6394 (1976), a specimen having a shape of a cylindrical column with a diameter of 50 mm and a height of 50 mm was prepared (N2-type specimen). A static spring constant (Ks (units: N/mm)) and a dynamic spring constant (Kd (units: N/mm 100 H)) of the specimen were measured, to thereby obtain dynamic multiplication (Kd/Ks 100 Hz).

The static spring constant (Ks) was calculated by, in conformity with JIS K 6385, compressing the specimen having the cylindrically columnar shape in a direction of the axis of the cylindrical column by 3 mm, and reading loads when distortion is 1 mm and 2 mm from a load spring diagram of second going.

The dynamic spring constant (Kd) was calculated by, in conformity with JIS K 6394, compressing the specimen having the cylindrically columnar shape in the direction of the axis of the cylindrical column by 1.5 mm (initial compressive strain is 3%), applying constant displacement vibration with an amplitude of ±0.05 mm by a frequency of 100 Hz from beneath with the position of 1.5 mm compression at the center (100 Hz ±0.1% dynamic strain), and measuring a dynamic load with a load cell attached to an upper portion of the specimen.

The dynamic multiplication (Kd/Ks) is a ratio between the static spring constant (Ks) and the dynamic spring constant (Kd). The smaller the dynamic multiplication (dynamic spring constant/static spring constant), the more excellent in vibration-insulating performance.

(Uneven Distribution Rate of Carbon Black and Silica)

A rubber composition having a compounding composition shown in later-described Table 1 is cut with a microtome to prepare slices with a thickness of 0.1 μm. The slice is observed by a transmission electron microscope (TEM) while regarding particles having a particle diameter of about 0.8 μm to about 1.2 μm as carbon black and particles having a particle diameter of about 10 nm to about 40 nm as silica, to measure the number of particles of carbon black and silica present in each of the phase of the rubber component (A) and the phase of the rubber component (B). Then, in each of the phase of the rubber component (A) (isoprene-based rubber) and the phase of the rubber component (B) (butadiene-based rubber), the ratio between the number of particles of carbon black and the number of particles of silica was obtained, and thereby the uneven distribution rate of carbon black and silica in each phase was obtained. It should be noted that the number of samples is 30 (n=30).

Examples 1 to 6, Comparative Examples 1 and 2

The durability and the dynamic characteristics were measured by using a rubber composition with a compound shown in Table 1. In addition, uneven distribution rate of carbon black and silica in the rubber component (A) and the rubber component (B) was measured. The results were shown in Table 1.

FIG. 2 is a transmission electron microscope (TEM) photograph of the rubber composition in Example 2. Example 2 is a rubber composition in which natural rubber (RSS)/polybutadiene rubber (BR)=60/40. As shown in FIG. 2, natural rubber (RSS) constitutes matrix portions of gray which is relatively light, while polybutadiene rubber (BR) constitutes insular portions (portions enclosed by broken lines) of gray which is relatively thick. It can be learned that carbon black (particle diameter of about 0.8 μm to about 1.2 μm) is unevenly distributed in the insular portions of relatively-thick gray constituted by polybutadiene rubber (BR), while silica (particle diameter of about 10 nm to about 40 nm) is unevenly distributed in the matrix portions of relatively-light gray constituted by natural rubber (RSS).

TABLE 1 Comparative Example Example 1 2 3 4 5 6 1 2 Rubber Component A RSS 80 60 40 30 60 60 60 60 IR — — — 30 — — — — Rubber Component B BR 20 40 60 40 40 40 40 40 Carbon Black 15 15 15 15 20 10 30 — Silica SW134 15 15 15 15 10 20 — 30 Other Zinc Oxide 5 5 5 5 5 5 5 5 Compounding Agents Stearic Acid 1 1 1 1 1 1 1 1 Oil 5 5 5 5 5 5 5 5 Antioxidant 6C 2 2 2 2 2 2 2 2 Antioxidant RD 2 2 2 2 2 2 2 2 Vulcanizing Series Sulfur 1 1 1 1 1 1 1 1 Accelerator CZ 2 2 2 2 2 2 2 2 Accelerator TT 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Uneven Distribution Rubber Component A 28 18 13 19 22 13 18 100 Rate (%) Rubber Component B 72 82 87 81 78 87 82 0 of Carbon Black Uneven Distribution Rubber Component A 86 84 72 84 86 76 0 82 Rate (%) of Silica Rubber Component B 14 16 28 16 14 24 100 18 Dynamic Characteristics Ks(N/mm) 192 201 195 202 194 200 194 202 Kd/Ks 1.44 1.40 1.38 1.39 1.38 1.40 1.38 1.40 Durability (10000's of units) 130 140 100 135 135 120 55 35

It should be noted that each component in Table 1 is as follows.

-   RSS: natural rubber -   IR: polyisoprene rubber, Nipol IR 2200 manufactured by Zeon     Corportion -   BR: polybutadiene rubber, Nipol BR 1250H manufactured by Zeon     Corporation -   Carbon black: SAEST S manufactured by Tokai Carbon Co., Ltd. -   SW134: silica treated by a polysulfide-based silane coupling agent,     manufactured by DAISO Co., Ltd. -   Oil: naphthenic processing oil, SUNTHENE 410 manufactured by Japan     Sun Oil Co., Ltd. -   Zinc oxide: zinc flower 3 -   Stearic acid: industrial stearic acid -   Antioxidant 6C: NOCRAC 6C manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Antioxidant RD: NOCRAC 224 manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Sulfur: colloidal sulfur -   Accelerator CZ: NOCCELER CZ manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Accelerator TT: NOCCELER TT manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd.

From the results shown in Table 1, it can be learned that the vibration-insulating rubber compositions to which the exemplary embodiments are applied (Examples 1 to 6) do not increase the dynamic multiplication (Kd/Ks) and are excellent in durability.

On the other hand, in a rubber composition in which silica is not compounded and only carbon black is compounded as a reinforcing agent (Comparative Example 1) and in a rubber composition in which carbon black is not compounded and only silica is compounded (Comparative Example 2), it can be learned that the durability is deteriorated.

(Ordinary State Characteristics)

With regard to a specimen prepared by heating the rubber composition with a compound shown in Table 2 at 170° C. for 15 minutes, vulcanizing to form a vulcanized sheet to be die-cut into a shape of dumbbell No. 3 (JIS K6251), 300% tensile stress (units: MPa) and elongation (units: %) were measured in conformity with JIS K6251/JIS K6253.

(Thermal Aging Resistance Test)

Similar to the case of the above-described ordinary state characteristics, a specimen having the shape of dumbbell No. 3 (JIS K6251) was prepared by use of the rubber composition with a compound shown in Table 2. In a tensile test of the specimen, a tensile tester equipped with a temperature controlled bath was used. In the temperature controlled bath of the tensile tester, an ambient atmosphere temperature of a jig that grasps the specimen is maintained at a predetermined temperature. After the specimen was set aside in the temperature controlled bath for a predetermined time, elongation and a change in elongation (units: %) were measured. The measuring condition is 100° C. by 1000 hours.

Examples 7 to 9, Comparative Examples 3 and 4

Ordinary state physical properties, the dynamic characteristics and the thermal aging resistance were measured by using a rubber composition with a compound shown in Table 2. The results are shown in Table 2.

It should be noted that each component in Table 2 is as follows.

-   RSS: natural rubber -   BR: polybutadiene rubber, Nipol BR 1250H manufactured by Zeon     Corporation -   Carbon black: SAEST S manufactured by Tokai Carbon Co., Ltd. -   SW134: silica treated by a polysulfide-based silane coupling agent,     manufactured by DAISO Co., Ltd. -   ER: silica treated by a silane-based surface treatment agent,     Aerosil R805 manufactured by Degussa -   Zinc oxide: zinc flower 3 -   Stearic acid: industrial stearic acid -   Antioxidant 6C: NOCRAC 6C manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Antioxidant RD: NOCRAC 224 manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Sulfur: colloidal sulfur -   Accelerator CZ: NOCCELER CZ manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd. -   Accelerator TT: NOCCELER TT manufactured by Ouchi Shinko Chemical     Industrial Co., Ltd.

TABLE 2 Comparative Example Example 7 8 9 3 4 Rubber RSS 50 80 80 80 80 Component BR 50 20 20 20 20 Carbon Black 14 14 14 14 14 Silica SW134 7 11 7 14 — ER 7 3 7 — 14 Other Zinc 5 5 5 5 5 Compound- Oxide ing Agent Stearic 1 1 1 1 1 Acid Anti- 2 2 2 2 2 oxidant 6C Anti- 2 2 2 2 2 oxidant RD Vulcanizing Sulfur 1 1 1 1 1 Series Acceler- 2 2 2 2 2 ator CZ Acceler- 0.5 0.5 0.5 0.5 0.5 ator TT Ordinary 300% 3.8 3.9 3.7 4.7 2.6 State Tensil Physical Stress Properties (Mpa) Elongation 583 643 631 611 704 (%) Dynamic Ks 159 153 153 161 118 Charac- (N/mm) teristics Kd/Ks 1.30 1.34 1.33 1.30 1.67 Heat Elongation 220 226 226 174 286 Resistance (%) Elongation −62 −65 −64 −72 −59 Change Rate (%)

From the results shown in Table 2, it can be learned that the vibration-insulating rubber compositions to which the exemplary embodiments are applied (Examples 7 to 9) indicate 300% tensile stress that is sufficient for the use as the vibration-insulating rubber, do not increase the dynamic multiplication (Kd/Ks), and are excellent in heat resistance (sufficient elongation after thermal aging, and small elongation change rate).

On the other hand, though the rubber composition (Comparative Example 3) in which only silica that is surface-treated by the polysulfide-based silane coupling agent is compounded as a silica component (SW134) indicates low dynamic multiplication (Kd/Ks), 300% stress is high, and elongation and elongation change rate after thermal aging are small; accordingly it can be learned that the heat resistance is deteriorated. Moreover, the rubber composition (Comparative Example 4) in which only silica that is surface-treated by the silane-based surface treatment agent is compounded as a silica component (ER) indicates increased dynamic multiplication (Kd/Ks); accordingly, it can be learned that the dynamic characteristics are not improved.

Reference Signs List

-   10 . . . Specimen -   11 . . . Metal internal cylinder -   12 . . . Metal external cylinder -   13 . . . Rubber elastic body -   14 . . . Bearing portion 

1. A vibration-insulating rubber composition comprising: a rubber component (A) comprising an isoprene-based rubber; a rubber component (B) comprising a butadiene-based rubber; a carbon black that is present mainly in the rubber component (B); and a silica that is present mainly in the rubber component (A).
 2. The vibration-insulating rubber composition of claim 1, wherein at least 70 wt % of a total amount of the carbon black is present in the rubber component (B), and at least 70 wt % of a total amount of the silica is present in the rubber component (A).
 3. The vibration-insulating rubber composition of claim 1, wherein the silica is modified by a silane coupling agent.
 4. The vibration-insulating rubber composition of claim 3, wherein the silane coupling agent is a polysulfide-based silane coupling agent.
 5. The vibration-insulating rubber composition of claim 1, comprising the rubber component (A) and the rubber component (B) in a weight ratio (A)/(B) in a range of 90/10 to 30/70.
 6. A vibration-insulating rubber composition comprising: a total amount of an isoprene-based rubber and a butadiene-based rubber that equals 100 parts by weight; 5 to 60 parts by weight of a carbon black; and 5 to 60 parts by weight of a silica, wherein at least 70% of a total amount of the carbon black is unevenly distributed in the butadiene-based rubber, and at least 70% of a total amount of the silica is unevenly distributed in the isoprene-based rubber.
 7. A vibration-insulating rubber composition comprising: a rubber component comprising an isoprene-based rubber and a butadiene-based rubber; and a reinforcing agent component comprising a carbon black and a silica, the rubber component and the reinforcing agent component being compounded, wherein the silica in the reinforcing agent component comprises: a silica (A) comprising silica particles whose surface has been surface-treated by a polysulfide-based silane coupling agent; and a silica (B) comprising silica particles whose surface has been surface-treated by a silane-based surface treatment agent.
 8. The vibration-insulating rubber composition of claim 7, wherein the silane-based surface treatment agent is an alkylsilane.
 9. The vibration-insulating rubber composition of claim 7, comprising the silica (A) and the silica (B) in a weight ratio (A)/(B) of (90/10) to (40/60).
 10. The vibration-insulating rubber composition of claim 7, wherein the silica (B) is a hydrophobically modified silica obtained by processing a surface of silica with an alkylsilane.
 11. The vibration-insulating rubber composition of claim 7, wherein the rubber component comprises the isoprene-based rubber and the butadiene-based rubber in a ratio in a range of 90/10 to 30/70.
 12. A vibration-insulating rubber composition comprising: a total amount of an isoprene-based rubber and a butadiene-based rubber that equals 100 parts by weight; 5 to 60 parts by weight of a carbon black; and 5 to 60 parts by weight of a silica, wherein the silica comprises: 40 to 90 wt % of a silica (A) that has been surface-treated by a polysulfide-based silane coupling agent, and 10 to 60 wt % of a silica (B) that has been surface-treated by an alkylsilane.
 13. The vibration-insulating rubber composition of claim 1, wherein the isoprene-based rubber comprises natural rubber, a polyisoprene rubber, or both.
 14. The vibration-insulating rubber composition of claim 1, wherein the isoprene-based rubber comprises natural rubber having a Mooney viscosity of 10 to
 200. 15. The vibration-insulating rubber composition of claim 1, wherein the isoprene-based rubber comprises natural rubber having a Mooney viscosity of 30 to
 100. 16. The vibration-insulating rubber composition of claim 1, wherein the butadiene-based rubber comprises at least one polybutadiene rubber selected from the group consisting of: a high cis-polybutadiene rubber having cis-1,4 coupling of about 90% or more, and a high vinyl-polybutadiene rubber having 1,2-coupling of about 10% or more.
 17. The vibration-insulating rubber composition of claim 16, wherein the polybutadiene rubber has a Mooney viscosity of 10 to
 100. 18. The vibration-insulating rubber composition of claim 16, wherein the polybutadiene rubber has a Mooney viscosity of 30 to
 70. 19. The vibration-insulating rubber composition of claim 1, comprising the rubber component (A) and the rubber component (B) in a weight ratio (A)/(B) in a range of 80/20 to 40/60.
 20. The vibration-insulating rubber composition of claim 1, comprising the rubber component (A) and the rubber component (B) in a weight ratio (A)/(B) in a range of 80/20 to 50/50. 